The effect of basal channels on oceanic ice-shelf melting

The presence of ice-shelf basal channels has been noted in a number
of Antarctic and Greenland ice shelves, but their impact on basal
melting is not fully understood. Here we use the Massachusetts
Institute of Technology general circulation model to investigate the
effect of ice-shelf basal channels on oceanic melt rate for an
idealized ice shelf resembling the floating tongue of Petermann
Glacier in Greenland. The introduction of basal channels prevents the
formation of a single geostrophically balanced boundary current;
instead the flow is diverted up the right-hand (Coriolis-favored) side
of each channel, with a return flow in the opposite direction on the
left-hand side. As the prescribed number of basal channels is
increased the mean basal melt rate decreases, in agreement with
previous studies. For a small number of relatively wide channels the
subice flow is found to be a largely geostrophic horizontal
circulation. The reduction in melt rate is then caused by an increase
in the relative contribution of weakly melting channel crests and
keels. For a larger number of relatively narrow channels, the subice
flow changes to a vertical overturning circulation. This change in
circulation results in a weaker sensitivity of melt rates to channel
size. The transition between the two regimes is governed by the Rossby
radius of deformation. Our results explain why basal channels play an
important role in regulating basal melting, increasing the stability
of ice shelves.